S E M I N A R S
SUMMER SEMINARS 2006 |
Tuesday, September 19th, 10:30 AM Search for the rare decay B -> pi l+l- at BABAR Ingrid Ofte (SLAC) The rare decay B -> pi l+ l- is the simplest manifestation of a b -> d l+ l- flavor-changing neutral current (FCNC) process. Like the b -> s l+ l- transition which has already been extensively studied experimentally, this process is sensitive to physics at the electroweak scale and can be used to constrain parameters of the standard model and its extensions. B -> pi l+ l- events have never yet been observed, and never before been searched for at any of the B-Factory experiments. At the BABAR experiment, we have recently performed a search for these decays in 230 million pairs of B-antiB mesons collected between 1999 and 2004. No evidence for B -> pi l+ l- was seen, but an upper limit on the branching fraction was obtained. I will present the procedure and results of this search and, in light of the current experimental status of B -> Xs l+ l- and B -> K(*) l+ l- decays, discuss the prospects for future measurements of B -> pi l+ l- and B -> rho l+ l-. |
Tuesday, September 5th, 10:30 AM A New Measurement of the Ratio of W and Z Production at CDF Katherine Copic (Fermilab / University of Michigan) |
Friday, August 11th, 10:30 AM Guido Barbiellini (Physics Department, University of Trieste, Italy) Stochastic Wake Field Acceleration (WFA) and Cosmic Gamma Ray Bursts The Wake Field Acceleration analogy between laboratory and cosmic plasmas may explain some of the observed correlations in gamma-ray bursts, namely between the collimation of the outflow, the total emitted energy, and the energy emitted in gamma-rays. The hypothesis that the photons are emitted during the acceleration and modulation of the leptons in the plasma at 10 15 cm from the central engine provides a link between spectral properties, the total energy, and the collimation angle. The energy is constantly transmitted mainly within the collimation angle so that the burst afterglow properties are linked to the prompt emission, since a fraction of the prompt energy of the plasma produces the afterglow at larger distances. Applying the WFA formulas, the luminosity is naturally linked to the local particle density, so the historical wind activity of the GRB progenitor is related to the luminosity behavior of the afterglow. Experimental data from GRBs with measured redshifts and jet opening angles appear to support this hypothesis. |
Monday, August 7th, 10:00 AM Adam Gibson ( University of California, Berkeley/Lawrence Berkeley National Laboratory ) Measuring the Top Quark Mass at CDF The top quark, discovered just more than ten years ago, continues to be one of the chief points of interest on the energy frontier. Its unusually large mass, corresponding to a Yukawa coupling near unity, hints at a special role for the top quark. But, more to the point, this enormous mass causes the top to decay before hadronizing, allowing a measurement more precise than is possible for any other quark. So, the top quark is an important part of the enterprise of precision Electroweak physics, testing the consistency of the standard Model and predicting the mass of the putative Higgs boson. The top quark was discovered with the CDF and D0 detectors at Fermilab's Tevatron accelerator complex just more than ten years. Upgraded |
Tuesday, July 25, 11:00 AM Lei Wang (University of Maryland) |
Thursday, July 27, 11:00 AM Selected topics on open charm physics at CLEO-c Batbold Sanghi (Cornell University) The CLEO-c experiment at the Cornell Electron Storage Ring is collecting data at the psi(3770), which is about 40 MeV above the DDbar production threshold, and slightly higher center-of-mass energies to study D(s) meson decays. In my talk, I will give a brief overview of the CLEO-c open charm program and focus on the following topics: -- a measurement of absolute D hadronic branching fractions, including the reference D^0->K^- pi^+ and D+->K^-pi^+pi^+ modes, which are normalizing modes for most of B physics, and -- a measurement of absolute branching fractions and form factors in semileptonic D -> K e nu and D -> pi e nu, which we have used to test recent unquenched LQCD results for semileptonic form factors. |
Tuesday, July 18, 10:30 AM Wystan Benbow (Max Planck Institut fuer Kernphysik) The H.E.S.S experiment, an array of four imaging atmospheric-Cherenkov telescopes located in Namibia, is used to search the sky for astrophysical gamma-ray emission above ~100 GeV. The unprecedented sensitivity of H.E.S.S. has enabled many groundbreaking studies of both galactic & extragalactic phenomena. Due to their usefulness in unraveling the mysteries of the non-thermal universe, observations of Active Galactic Nuclei (AGN) comprise a major part of the scientific studies performed by H.E.S.S. (~30% of the total observations). An overview of the H.E.S.S. AGN program, its results, and future plans will be presented. |
SPRING QUARTER 2006 |
June 2006 |
Tuesday, June 13, 10:30 AM Recent Galactic results from HESS Stefan Funk (SLAC) The H.E.S.S. experiment (High Energy Stereoscopic System) is an array of imaging Cherenkov telescopes for the detection of gamma rays in the energy domain above 100 GeV. In its first two years of operation, H.E.S.S. has made a remarkable contribution to our understanding of gamma-ray sources and provided an unprecedented view on the inner part of our own Galaxy. In this talk I will report on recent Galactic H.E.S.S. results, including the new population of sources detected in the scan of the inner Galaxy and their possible multi-wavelength counterparts. Selected results will be shown on gamma-ray observations objects like Supernova remnants and Pulsar wind nebulae. |
Wednesday, June 7, 2:00 PM The Shy Lepton: Taus at D0 Silke Nelson Tau Leptons play a key role in the discovery potential of the Tevatron, which represents the current energy frontier with ppbar collisions at sqrt{s} = 1.96 TeV. However, the reconstruction and selection of tau decays is challenging at hadron colliders, requiring careful use of the detector to maximize sensitivity. The reconstruction and selection of hadronic tau decays using the D0 detector will be discussed in detail, along with the benchmark measurement of the cross-section of Z-bosons decaying to tau pairs. Recent results building upon this work to constrain new physics will also be presented. |
Tuesday, June 6, 10:30 AM Putting Pulsars on Scale Bulent Kiziltan (UCSC Astronomy Dept.) The number of radio pulsars and X-ray binaries for which reliable mass constraints are available has increased significantly in the last 10 years. We will review the methods currently used to estimate neutron star masses with the available mass estimates. Then, we will discuss the implications of the mass distribution to models of supernova explosions, stellar evolution, binary evolution and the equation of state of matter at nuclear densities. |
May 2006 |
Tuesday, May 30, 10:30 AM The Large Synoptic Survey Telescope Project Kirk Gilmore (Stanford/SLAC/KIPAC) The Large Synoptic Survey Telescope (LSST) will be a large, wide-field ground based telescope designed to obtain sequential images of the entire visible sky every few nights. The optical design involves a 3-mirror system with an 8.4 m primary, which feeds three refractive correcting elements inside a camera, providing a 10 square degree field of view sampled by a 3 Gpixel focal plane array. The total effective system throughput, is nearly two orders of magnitude larger than that of any existing facility. The survey will yield contiguous overlapping imaging of 20,000 - 23,000 square degrees of sky in 6 optical bands covering the wavelength regime of 350-1100 nm. The LSST facility and my presentation is organized in five sections; Science, project management, telescope, camera and data management/data acquisition. I will briefly touch on each of these subjects with some emphasis on the current status of the R&D of the camera. |
Tuesday, May 23, 10:30 AM Nate Bezayiff (SCIPP ) Recently a transistion layer model has been proposed that if validated may provide a new method of determining a black hole's mass. The first step in this method would be to obtain a monotonic curve relating a compact object's energy spectrum power law indices (PLI) to its power density quasi-periodic oscillations (QPO). The second step would require shifting from a PLI-QPO curve of a black hole of known mass to the PLI-QPO curve of a black hole of unknown mass. From this shift, which should only depend on the ratio between the masses of the two black holes, one should be able to determine the mass of the unknown black hole. We evaluated the transition layer model for two black holes of unknown mass, GRS1758-258 and GX339-4. The transition layer model appeared to apply well to GRS1758-258 (9.3+.05-3.0M) but requires some modification in the case of GX339-4 (2-3M). We have concluded that the transition layer model requires constraining several free parameters that make the shift between PLI-QPO curves of different black hole masses more complicated than the simple mass ration of the two compact objects. |
Tuesday, May 16, 10:30 AM - CANCELED! Title: TBD Stefan Funk (SLAC) |
Tuesday, May 9th, 10:30 AM Nearby, Thermally Emitting Neutron Stars: Laboratories for Extreme Physics David Kaplan (MIT) Neutron stars, born when massive stars die in spectacular supernova explosions, are among the densest objects in the universe. Their centers are so dense and complicated that detailed calculations are largely out of reach of theoretical physics, with a wide variety of compositions and structures possible. Observations of neutron stars may therefore be the best way to constrain the behavior of matter in these extreme conditions. I will describe how we are using observations with a variety of ground- and space-based telescopes to try to pin down the basic parameters of neutron stars. Specifically, I will discuss how we are measuring their sizes and cooling rates and how these measurements may influence our understanding of basic physics. |
April 2006 |
Thursday, April 27th, 2:00 PM Fluctuations with WA98 and STAR experiment Gopika Sood (Valparaiso University) The temporary restoration of chiral symmetry and its subsequent breaking may result in the formation of domains of disoriented chiral condensate (DCC) in which the average chiral order parameter differs from its surrounding vacuum. This domain formation is expected to modify the multiplicity distribution of neutral and charged pions (according to the relation, P= 1 /2 sqrt f ) and disturb the electromagnetic and hadronic energy ratio in the h - f phase space. Based upon the neutral pion fraction and the energy ratio, events are characterized as “centauro” and “Anti-Centauro.” The events for which the density of charged particles is greater that that of neutral pions (i.e, hadronic energy larger that electromagnetic) are labelled as centauro and the events for which the electromagnetic energy is greater than hadronic energy are Anti-Centauro. The neutral pion fraction and the energy ratio are the measures used to study DCC type fluctuations. The data from WA98 (Pb+Pb @ 158 A GeV) and STAR (Au+Au @ 62 and 200 GeV) experiments is analyzed and some events are filtered which show anomalous fluctuations in neutral pion fraction or in energy ratio. |
Wednesday, April 26th, 1:00 PM Searches for rare Bs Decays with the DØ Detector Ralf Bernhard (University of Zürich) Experimental upper limits are presented for searches for the rare flavour changing neutral current decays Bs -> Mu+ Mu- and Bs -> Phi Mu + Mu-. A data set with integrated luminosity of up to 1 fb^-1 of proton-antiproton collisions at sqrt(s)=1.96 TeV collected with the DO detector in RunII of the Fermilab Tevatron collider is used. The decay mode Bs -> Mu+ Mu- is particularly sensitive to supersymmetric extensions of the Standard Model. Therefore the obtained upper limit is a powerful input variable to constrain these models. For example In models where the lightest supersymmetric particle is considered to be a dark matter candidate the limit aids in restricting the dark matter scattering cross section on nucleons. The exclusive FCNC decay Bs -> Phi Mu+ Mu- is related to the quark-level transition of b -> s l l. The corresponding decays in the Bd and B+ system have been already measured at B-factories and were found to be consistent with the SM within the present experimental uncertainties. An observation of this decay or experimental upper limit on its rate will yield additional important information on the flavor dynamics of FCNC decays. In addition to the searches for flavour changing neutral current decays, the result of the observation of the decay Bs -> Psi(2S) Phi is presented. |
Tuesday, April 25th, 10:30 AM - CANCELED! The Large Synoptic Survey Telescope Project Kirk Gilmore (Stanford/SLAC/KIPAC) The Large Synoptic Survey Telescope (LSST) will be a large, wide-field ground based telescope designed to obtain sequential images of the entire visible sky every few nights. The optical design involves a 3-mirror system with an 8.4 m primary, which feeds three refractive correcting elements inside a camera, providing a 10 square degree field of view sampled by a 3 Gpixel focal plane array. The total effective system throughput, is nearly two orders of magnitude larger than that of any existing facility. The survey will yield contiguous overlapping imaging of 20,000 - 23,000 square degrees of sky in 6 optical bands covering the wavelength regime of 350-1100 nm. The LSST facility and my presentation is organized in five sections; Science, project management, telescope, camera and data management/data acquisition. I will briefly touch on each of these subjects with some emphasis on the current status of the R&D of the camera. |
Monday, April 24th, 11:00 AM Robust predictions of LHC and cosmic ray cross sections/ saturating the Froissart bound Martin Block (Northwestern University) There will not be an abstract for this seminar |
Tuesday, April 11th, 10:30 AM MOND versus Dark Matter Update Gary Godfrey (SLAC) The simple MOND ansatz of setting the acceleration of gravity a=sqrt(anewton*a0) when a<<a0, explains a spectacular wide range of regularities in bound gravitational systems. These systems range in size from 10**6 solar mass dwarf galaxies to 10**14 solar mass galactic clusters. The constant a0=1.2 x 10**-8 cm/sec2 is the same for all systems, and the only variable in describing the various effects (such as rotation curves) is the baryonic M/L which turns out to be of order 1 for all fits. Mystically, the value of a0 is close to the Hubble constant H0=7 x 10**-8 cm/sec2. |
Wednesday, April 5th, 1:00 PM First observation of Bs to Psi(2S) phi and first measurement of the relative branching fractions Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) Daejung Kong (Fermilab) I report the first observation of Bs to Psi(2S) phi signals using 360 pb^{-1} of the Tevatron Run II data sample, where Psi(2S) decays into mu+mu- and J/psi pi+pi- mode, and with phi decaying to K+K-. I also report the measurement of the relative branching ratio of Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) using the J/psi, Psi(2S) to mu+mu- decay mode. |